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The Daily Vet by petMD

The Daily Vet is a blog featuring veterinarians from all walks of life. Every week they will tackle entertaining, interesting, and sometimes difficult topics in the world of animal medicine – all in the hopes that their unique insights and personal experiences will help you to understand your pets.

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The isoflavones and isoflavonoids found in soybeans have long been known to have antioxidant properties that decrease the tissue damage of normal cell metabolism. It is also known that human populations that consume foods high in these organic compounds have lower incidences of breast cancer and other common cancers. Now veterinary scientists have found that isoflavones fed to dogs increases daily energy expenditure and reduces body fat accumulation without a reduction in calorie intake.

What are Isoflavones?

Isoflavones are found naturally in soybeans. Green beans, alfalfa sprouts, mung bean sprouts, cowpeas, kudzu root and red clover also contain these organic chemicals. Even highly processed foods like tofu retain isoflavones and the fermenting of miso (a soy derived paste used in Chinese and Japanese dishes) actually increases isoflavones. Isoflavones help protect their parent plant from fungal and bacterial diseases. The isoflavones in soybeans also stimulate soil organism to form the nitrogen absorbing root nodules that promote the protein storing capacity of these food sources.

Cancer prevention is believed to result from the estrogen-like properties of isoflavones that interferes with breast cancer cell growth. This hormonal influence is also though to interfere with the metabolism and biological activity of other types of cancer cells. These cancer protecting properties of isoflavones are believed to be the reason that the incidence of breast cancer is much lower in human cultures where soybeans and mung beans are a large part of the normal diet. It is this estrogen hormone activity that may also influence pet obesity.

Isoflavones and Fat in Dogs

Veterinary researchers studied two groups of spayed/neutered Labrador Retrievers, a dog breed notorious for having tendencies toward obesity after sexual alteration (i.e., neutering/spaying). The diet for both groups was identical in protein, fat, carbohydrate and calorie content. The only difference was that one diet contained isoflavones and the other contained none. The dogs were fed 25 percent more than their calculated daily energy requirement for nine months, as they were being monitored for their energy or calorie expenditure and percentage of body fat. The isofalvone group had significantly greater energy expenditure and reduced body fat accumulation at the end of the nine month period. The researchers attributed the results to the estrogen-like activity of the isoflavones.

The elimination or reduction of sex hormones in spayed or neutered dogs is known to significantly reduce energy expenditure in pets. This study suggests that the supplementation of natural estrogen compounds like isoflavones reverses this energy metabolism decline and may prevent obesity in sexually altered pets.

Soy Products and Dog Food

The findings in this study are compelling for the addition of soy products to commercial pet food. Unfortunately soy is not likely to become commonplace in pet food in the near future.

Although soy protein is found in some premium pet foods, it is not a common ingredient in most commercial dog foods. The obvious reason for this is cost. Soybeans and soybean products are a large part of the diet for many countries and cultures that are unable to produce an adequate supply for their own population. Soy containing products are also popular in the U.S. and other Western countries despite not being a staple of the normal western diet. This worldwide demand for U.S. produced soybeans increases the price. Commercial pet food is extremely price sensitive. To maintain target price points and consumer loyalty, commercial pet food companies must substitute less expensive sources of protein.

The bright side, however, is that the study was funded by a major pet food company, which suggests that they will be rolling out a product with significant soy or isoflavone content. I am pursuing contact with them and the researchers and I will keep you posted. In the meantime, consult your veterinarian about how you might incorporate soybeans, tofu or miso into your dog’s diet.

Dr. Ken Tudor

Image: vegetarian by 8 Kome / via Flickr

Comments  6

Leave Comment
  • Carbs
    05/31/2012 07:20am

    Wouldn't soy beans be high in carbohydrates which turn into sugars?

    How can the study be sure the dogs didn't have a higher energy level due to the carbs?

  • TheOldBroad
    05/31/2012 11:20am

    Both diets contained the exact same amount of carbohydrate, soy or grain, so the sugar levels would be identical in both diets. I think you may be confusing the idea of "sugar high" after eating simple sugars vs. normal complex carbohydrate consumption of normal meals.

    Dr. T

  • Another great post
    05/31/2012 08:29pm

    Thank you, Dr. Tudor, for another great post. I have been wondering, "Gee, how much more info. can there be about cat and dog weight loss?" You just keep coming with the great info.

    Thank you for this latest, very interesting read!

  • 3Dogs1Cat
    05/31/2012 10:29pm

    Thank you so much for your kind thoughts and your continued readership. I think you and TheOldBroad are my only readers but I am content with that. You both are great and I enjoy your comments even though I don't always reply. Your observations are excellent, informative and often don't need my input. They stand on their own merits. Thanks again.
    Dr. T

  • 06/03/2012 08:28am

    "The diet for both groups was identical in protein, fat, carbohydrate and calorie content. The only difference was that one diet contained isoflavones and the other contained none."

    In the form of food or supplements?

    As for isoflavones and breast cancer, it's a mixed bag:
    http://breastcancer.about.com/od/riskfactorsindetail/a/soy_bc_diet_2.htm
    The American Cancer Society says that concentrated extracts of soy isoflavones may encourage tumor growth, and should be avoided. Women in the Japanese study who had the lowest rates of breast cancer had consumed soy from childhood, or at least from pre-puberty. Post-menopausal women should not overdo soy products, because the powerful isoflavones mimic natural estrogen, which fuels 80% of all cases of breast cancer.

    Could the dogs have lost weight because soy was so irritating to the gut it sped everything through?

    I await the study.

    Personally I avoid cat food with soy products.

  • CathyA
    06/03/2012 02:04pm

    You are absolutely right about differing opinions on breast cancer and naturally occuring estrogens in food. Much more study is necessary. The same is also true of the effect of isoflavones and fat production. To my knowledge this is one of the first articles on the subject. Much more research is needed to make absolute statements but these results are certainly intriguing. The abstract is not clear what the source of the isoflavones were so I also await publication of the article to find if it was indeed soy or isolated isoflavone supplement. Small to moderate amounts of soy (which is all that is required to achieve necessary isoflavone levels) is not "irritating to the gut and speeds everything through" Dietary fiber is the more important nutrient for gut transit time. Just because something contains soy doesn't mean it is necessarily more fibrous. Also energy and nutrient absorption is based on many other factors much more important than transit time. That is why diet pet foods that contain high fiber content can still deliver necessary or excess energy. In fact, most fat pets are eating high fiber diets and gaining, not losing weight. Soy products are a great food, have a smaller carbon footprint and environmental impact than livestock and actually fix nitrogen to the soil for other crops so less fertilizer is necessary. They are not my first choice for cat food but they are not taboo.
    Dr. T

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